Distributed database management system

ABSTRACT

A distributed database management system provides a central database resident on a server that contains database objects. Objects, e.g., program guide data, to be replicated are gathered together into distribution packages called “slices,” that are transmitted to client devices. A slice is a subset of the central database which is relevant to clients within a specific domain, such as a geographic region, or under the footprint of a satellite transmitter. The viewer selects television programs and Web content from displayed sections of the program guide data which are recorded to a storage device. The program guide data are used to determine when to start and end recordings. Client devices periodically connect to the server using a phone line and upload information of interest which is combined with information uploaded from other client devices for statistical, operational, or viewing models.

PRIORITY CLAIM

This application claims benefit, under 35 U.S.C. § 120, as aContinuation of application Ser. No. 14/550,857, filed Nov. 21, 2014,which is a Continuation of application Ser. No. 13/934,084, filed Jul.2, 2013, which is a Continuation of application Ser. No. 10/828,921,filed Apr. 20, 2004 (issued as U.S. Pat. No. 8,478,114 on Jul. 7, 2013),which is a Continuation of application Ser. No. 09/422,139, filed Oct.20, 1999 (issued as U.S. Pat. No. 6,728,713 on Apr. 27, 2004), whichfurther claims benefit, under 35 U.S.C. § 119(e), of ProvisionalApplication Ser. No. 60/127,178, filed Mar. 30, 1999, the entirecontents of each of which is hereby incorporated by reference as iffully set forth herein. The applicant(s) hereby rescind any disclaimerof claim scope in the parent application(s) or the prosecution historythereof and advise the USPTO that the claims in this application may bebroader than any claim in the parent application(s).

BACKGROUND Technical Field

The invention relates to the storing and viewing of television programmaterial in a computer environment. More particularly, the inventionrelates to the storage, distribution, and maintenance of information ina distributed self-maintaining database management system in a computerenvironment.

Description of the Prior Art

A classic tension exists in the design of automated data processingsystems between pure client-server based systems, such as computermainframe systems or the World Wide Web, and pure distributed systems,such as Networks of Workstations (NOWS) that are used to solve complexcomputer problems, such as modeling atomic blasts or breakingcryptographic keys.

Client-server systems are popular because they rely on a clean divisionof responsibility between the server and the client. The server is oftencostly and specially managed, since it performs computations or storesdata for a large number of clients. Each client is inexpensive, havingonly the local resources needed to interact with the user of the system.A network of reasonable performance is assumed to connect the server andthe client. The economic model of these systems is that of centralizedmanagement and control driving down the incremental cost of deployingclient systems.

However, this model has significant costs that must be considered. Forinstance, the incremental cost of adding a new client system may bequite high. Additional network capacity must be available, sufficientcomputing resources must be available to support that client, includingstorage, memory and computing cycles, and additional operationaloverhead is needed for each client because of these additionalresources. As the central servers become larger and more complex theybecome much less reliable. Finally, a system failure of the serverresults in all clients losing service.

Distributed systems are popular because the resources of the system aredistributed to each client, which enables more complex functionalitywithin the client. Access to programs or data is faster since they arelocated with the client, reducing load on the network itself. The systemis more reliable, since the failure of a node affects only it. Manycomputing tasks are easily broken down into portions that can beindependently calculated, and these portions are cheaply distributedamong the systems involved. This also reduces network bandwidthrequirements and limits the impact of a failed node.

On the other hand, a distributed system is more complex to administer,and it may be more difficult to diagnose and solve hardware or softwarefailures.

Television viewing may be modeled as a client-server system, but onewhere the server-to-client network path is for all intents and purposesof infinite speed, and where the client-to-server path is incoherent andunmanaged. This is a natural artifact of the broadcast nature oftelevision. The cost of adding another viewer is zero, and the servicedelivered is the same as that delivered to all other viewers.

There have been, and continue to be, many efforts to deliver televisionprogramming over computer networks, such as the Internet, or even over alocal cable television plant operating as a network. The point-to-pointnature of computer networks makes these efforts unwieldy and expensive,since additional resources are required for each additional viewer.Fully interactive television systems, where the viewer totally controlsvideo streaming bandwidth through a client settop device, have proveneven more uneconomical because dedication of server resources to eachclient quickly limits the size of the system that can be profitablybuilt and managed.

However, television viewers show a high degree of interest in choice andcontrol over television viewing.

It would be advantageous to provide a distributed database managementsystem that enables a client to easily maintain the data in its localdatabase and to synchronize said database with the main server database.It would further be advantageous to provide a distributed databasemanagement system that provides a secure data transmission link betweena server and its clients.

SUMMARY

The invention provides a distributed database management system. Thesystem creates a self-maintaining distributed database system thatensures that a consistent subset of a central database is replicated inany number of client devices. In addition, the invention provides asystem that ensures that data transmissions between a server and clientare secure.

A client device, such as a digital video recorder (DVR), typified inU.S. Pat. No. 6,233,389 B1, owned by the Applicant and incorporatedherein by reference, provides functionality typically associated withcentral video servers, such as storage of a large amount of videocontent, ability to choose and play this content on demand, and full“VCR-like” control of the delivery of the content, as typified in U.S.Pat. No. 6,327,418 B1, owned by the Applicant and incorporated herein byreference.

The invention provides a central database resident on a server thatcontains database objects. Objects (e.g., program guide data objects) tobe replicated are gathered together into distribution packages called“slices.” A slice is a subset of the central database which is relevantto clients within a specific domain, such as a geographic region, orunder the footprint of a satellite transmitter.

Using standard, currently existing techniques, ranging from private datachannels in digital television signals, through modulation of data ontothe Vertical Blanking Interval (VBI) of an analog television signal, todirect connection with the server using a modem, slices are transmittedto the client devices, which choose portions of the information to savelocally.

The speed and periodicity of traversing the central database andgenerating slices for transmission is adjustable in an arbitrary fashionto allow useful cost/performance tradeoffs to be made. A slice istransmitted by breaking the encrypted slice into a succession of short,numbered data packets. Each slice is encrypted using a short-livedsymmetric key before being transmitted to client devices.

When a connection between the central database and a client device isestablished, the client device sends an inventory of previously receivedslices to a transmission server. The transmission server compares theinventory with the list of slices that should have been processed by theclient. Slices which were not processed are then transmitted to theclient.

A slice may communicate service related data to a client device orcontain an authorization object indicating the allowable time delaybefore another authorization object is received, as well as one or moresymmetric keys used to decrypt new slices which are valid for a shorttime period.

If the client has not received a proper authentication object by thedelay time set in the client's local database, then the client willcommence denial of select services to the viewer.

Preference objects are created based on direct and indirect preferencesand are weighted. A list of preferred programs is generated using thepreference objects. The list is used to create a recording schedulewhich is a collection of recorded programs of most interest to theviewer.

Specific sections of the program guide are displayed to the viewer,e.g., sorted by time, station, network, genre, director, actor, etc. Theviewer scrolls through the guide data to find program material ofinterest. The viewer selects television programs and Web content fromthe program guide data. The selected television programs and Web contentare used to create a recording schedule which is used to schedulerecordings to a storage device. The program guide data are used todetermine when to start and end recordings. The client device tunes tothe correct television station or URL to record the scheduled programmaterial.

Client devices periodically connect to the server and upload informationof interest, such as viewing patterns, inferred characteristics,operational data or transactional information relating to the viewer'spurchase requests. This information is combined with informationuploaded from other client devices to enhance the service by improvingstatistical models, focusing resources on those programs and services ofmost interest to the viewers, or alerting the service provider topotential operational problems in the client device, such as failingcomponents.

Other aspects and advantages of the invention will become apparent fromthe following detailed description in combination with the accompanyingdrawings, illustrating, by way of example, the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram of a preferred embodiment of adistributed television viewing management system according to theinvention;

FIG. 2 is a block schematic diagram of the structure of a viewing objectin computer storage for programmatic access according to the invention;

FIG. 3 is a block schematic diagram showing how the schema for a viewingobject is structured in computer storage for programmatic accessaccording to the invention;

FIG. 4 is a block schematic diagram showing an example graph ofrelationships between viewing objects which describe information aboutprograms according to the invention;

FIG. 5 is a block schematic diagram showing an example graph ofrelationships generated when processing viewer preferences to determineprograms of interest according to the invention;

FIG. 6 is a block schematic diagram showing the scheduling of inputs andstorage space for making recordings according to the invention;

FIG. 7 is a flowchart showing the steps taken to schedule a recordingusing the mechanism depicted in FIG. 6 according to the invention;

FIG. 8 is a block schematic diagram of a preferred embodiment of theinvention showing the bootstrap system configuration according to theinvention;

FIG. 9a is a block schematic diagram of the decision flowchart for thebootstrap component according to the invention;

FIG. 9b is a block schematic diagram of the decision flowchart for thebootstrap component according to the invention; and

FIG. 10 is a block schematic diagram of the decision flowchart for thesoftware installation procedure according to the invention.

DETAILED DESCRIPTION

The invention is embodied in a distributed database management system ina computer environment. A system according to the invention creates aself-maintaining distributed database system that ensures that aconsistent subset of a central database is replicated in any number ofclient devices. In addition, the invention provides a system thatensures that data transmissions between a server and client are secure.

The invention is embodied in a television viewing informationtransmission and collection system that improves the ability of theindividual viewer to select and automatically timeshift televisionprograms while providing opportunities for a service provider to enhanceand direct the viewing experience. The invention describes a systemwhich is fully distributed, in that calculations pertaining to anindividual viewer are performed personally for that viewer within alocal client device, while providing for the reliable aggregation anddissemination of information concerning viewing habits, preferences orpurchases.

The Database of Television Viewing Information

FIG. 1 gives a schematic overview of the invention. Central to theinvention is a method and apparatus for maintaining a distributeddatabase of television viewing information among computer systems at acentral site 100 and an extremely large number of client computingsystems 101. The process of extracting suitable subsets of the centralcopy of the database is called “slicing” 102, delivering the resulting“slices” to clients is called “transmission” 103, delivering informationcollected about or on behalf of the viewer to the central site is called“collection” 104, and processing the collected information to generatenew television viewing objects or reports is called “analysis” 107; inall cases, the act of recreating an object from one database withinanother is called “replication” 105. Data items to be transmitted orcollected are termed “objects” 106, and the central database and eachreplicated subset of the central database contained within a clientdevice is an “object-based” database. The objects within this databaseare often termed “television viewing objects”, “viewing objects”, orsimply “objects”, emphasizing their intended use. However, one skilledin the art will readily appreciate that objects can be any type of data.

The viewing object database provides a consistent abstract softwareaccess model for the objects it contains, independent of and in parallelwith the replication activities described herein. By using thisinterface, applications may create, destroy, read, write and otherwisemanipulate objects in the database without concern for underlyingactivities and with assurance that a consistent and reliable view of theobjects in the database and the relationships between them is alwaysmaintained.

Basic Television Viewing Object Principles

Referring to FIG. 2, television viewing objects are structured as acollection of “attributes” 200. Each attribute has a type 201, e.g.,integer, string or boolean, and a value 202. All attribute types aredrawn from a fixed pool of basic types supported by the database.

The attributes of an object fall into two groups: “basic” attributes,which are supplied by the creator or maintainer of the viewing object;and “derived” attributes, which are automatically created and maintainedby mechanisms within the database. Basic attributes describe propertiesof the object itself; derived attributes describe the relationshipsbetween objects. Basic attributes are replicated between databases,whereas derived attributes are not.

With respect to FIG. 3, there is a small set of fundamental object typesdefined by the invention; each object type is represented as a specificset of related attributes 300, herein called a “schema”. The schemadefines a template for each attribute type 301, which includes the type302 and name of the attribute 303. Actual television viewing objects arecreated by allocating resources for the object and assigning values tothe attributes defined by the schema. For example, a “program” schemamight include attributes such as the producer, director or actors in theprogram, an on-screen icon, a multi-line description of the programcontents, an editorial rating of the program, etc. A physical programobject is created by allocating storage for it, and filling in theattributes with relevant data.

There is one special object type predefined for all databases called theschema type. Each schema supported by the database is represented by aschema object. This allows an application to perform “introspection” onthe database, i.e., to dynamically discover what object types aresupported and their schema. This greatly simplifies application softwareand avoids the need to change application software when schemas arechanged, added or deleted. Schema objects are handled the same as allother viewing objects under the methods of this invention.

Referring again to FIG. 2, each object in a database is assigned an“object ID” 203 which must be unique within the database. This object IDmay take many forms, as long as each object ID is unique. The preferredembodiment uses a 32-bit integer for the object ID, as it provides auseful tradeoff between processing speed and number of unique objectsallowed. Each object also includes a “reference count” 204, which is aninteger giving the number of other objects in the database which referto the current object. An object with a reference count of zero will notpersist in the database (see below).

One specific type of viewing object is the “directory” object. Adirectory object maintains a list of object IDs and an associated simplename for the object. Directory objects may include other directoryobjects as part of the list, and there is a single distinguished objectcalled the “root” directory. The sequence of directory objects traversedstarting at the root directory and continuing until the object ofinterest is found is called a “path” to the object; the path thusindicates a particular location within the hierarchical namespacecreated among all directory objects present in the database. An objectmay be referred to by multiple paths, meaning that one object may havemany names. The reference count on a viewing object is incremented byone for each directory which refers to it.

Methods for the Maintenance of Database Consistency and Accuracy

One of the features of a preferred embodiment of the invention is toinsure that each database replica remains internally consistent at alltimes, and that this consistency is automatically maintained withoutreference to other databases or the need for connection to the centralsite. There is no assurance that transmission or collection operationshappen in a timely manner or with any assured periodicity. For instance,a client system may be shut off for many months; when a transmission tothe system is finally possible, the replication of objects must alwaysresult in a consistent subset of the server database, even if it is notpossible to transmit all objects needed to bring the central and clientdatabases into complete synchronization.

Even more serious, there can be no guarantee of a stable operationalenvironment while the database is in use or being updated. For example,electrical power to the device may cease. This invention treats alldatabase updates as “transactions”, meaning that the entire transactionwill be completed, or none of it will be completed. The specifictechnique chosen is called “two-phase commit”, wherein all elements ofthe transaction are examined and logged, followed by performing theactual update. One familiar in the art will appreciate that a standardjournaling technique, where the transaction is staged to a separate log,combined with a roll-forward technique which uses the log to repeatpartial updates that were in progress when the failure occurred, issufficient for this purpose.

One required derived attribute of every object is the “version”, whichchanges with each change to the object; the version attribute may berepresented as a monotonically increasing integer or otherrepresentation that creates a monotonic ordering of versions. The schemafor each object that may be replicated includes an attribute called“source version” which indicates the version of the object from whichthis one was replicated.

Transmission of a viewing object does not guarantee that every clientreceives that object. For instance, while the object is being broadcast,external factors such as sunspots, may destroy portions of thetransmission sequence. Viewing objects may be continually retransmittedto overcome these problems, meaning that the same object may bepresented for replication multiple times. It is inappropriate to simplyupdate the database object each time an object to be replicated isreceived, as the version number will be incremented although no changehas actually occurred. Additionally, it is desirable to avoid initiatinga transaction to update an object if it is unnecessary; considerablesystem resources are consumed during a transaction.

Two approaches are combined to resolve this problem. First, most objectswill have a basic attribute called “expiration”. This is a date and timepast which the object is no longer valid, and should be discarded. Whena new object is received, the expiration time is checked, and the objectdiscarded if it has expired. Expiration handles objects whosetransmission is delayed in some fashion, but it does not handle multiplereceptions of the same unexpired object.

The source version attribute handles this problem. When a viewing objectis transmitted, this attribute is copied from the current versionattribute of the source object. When the viewing object is received, thesource version of the received object is compared with the sourceversion of the current object. If the new object has a higher sourceversion attribute, it is copied over the existing object, otherwise itis discarded.

It is assumed that a much greater number of viewing objects aretransmitted than are of interest to any particular client system. Forexample, a “channel” viewing object which describes the channels on aparticular cable system is of no interest to clients attached to othercable systems. Because of the overhead of capturing and adding newobjects to the database, it would be advantageous for received objectsto be filtered on other attributes in addition to those described above.The invention accomplishes this by using a filtering process based onobject type and attribute values. In one implementation, this filteringprocess is based on running executable code of some kind, perhaps as asequence of commands, which has been written with specific knowledge ofvarious object types and how they should be filtered.

In a preferred embodiment of the invention, a “filter” object is definedfor each object type which indicates what attributes are required,should not be present, or ranges of values for attributes that make itacceptable for addition to the database. One skilled in the art willreadily appreciate that this filter object may contain executable codein some form, perhaps as a sequence of executable commands. Thesecommands would examine and compare attributes and attribute values ofobject being filtered, resulting in an indication of whether the objectshould be the subject of further processing.

Viewing objects are rarely independent of other objects. For example, a“showing” object (describing a specific time on a specific channel) isdependent on a “program” object (describing a specific TV program). Oneimportant aspect of maintaining consistency is to insure that alldependent objects either already exist in the database or are to beadded as part of a single transaction before attempting to add a newviewing object. This is accomplished using a basic attribute of the newviewing object called the “dependency” attribute, which simply lists theobject IDs and source versions of objects that the new object isdependent on. Clearly, new versions of an object must be compatible, inthe sense that the schema defining new versions be the same or have astrict superset of the attributes of the original schema.

When a new viewing object is received, the database is first checked tosee if all dependencies of that object are present; if so, the object isadded to the database. Otherwise, the new object is “staged”, saving itin a holding area until all dependent objects are also staged. Clearly,in order for a new set of viewing objects to be added to the database,the dependency graph must be closed between objects in the staging areaand objects already existing in the database, based on both object IDand source version. Once closure is achieved, meaning all dependentobjects are present, the new object(s) are added to the database in asingle atomic transaction.

Naming and Finding Television Viewing Objects

Directory objects have been described previously. Referring to FIG. 4,the collection of directory objects, and the directed graph formed bystarting at the root path 400 and enumerating all possible paths toviewing objects is called a “namespace”. In order for an object to befound without knowing a specific object ID, one or more paths withinthis namespace must refer to it. For instance, application software haslittle interest in object IDs, instead the software would like to referto objects by paths, for instance “/tvschedule/today”. In this example,the actual object referred to may change every day, without requiringchanges in any other part of the system.

One way in which a path to an object may be established is by specifyinga “pathname” basic attribute on the object. The object is added to thedatabase, and directory objects describing the components of the pathare created or updated to add the object. Such naming is typically usedonly for debugging the replication mechanisms. Setting explicit paths isdiscouraged, since the portions of the central database replicated oneach client system will be different, leading to great difficulty inmanaging pathnames among all replicas of the database.

A preferred method for adding an object to the database namespace iscalled “indexing”. In a preferred embodiment of the invention, an“indexer” object is defined for each object type which indicates whatattributes are to be used when indexing it into the database namespace.One skilled in the art will readily appreciate that this indexer objectmay contain executable code in some form, perhaps as a sequence ofexecutable commands. These commands would examine and compare attributesand attribute values of object being indexed, resulting in an indicationof where the object should be located in the namespace.

Based on the object type, the indexer examines a specific set ofattributes attached to the object. When such attributes are discoveredthe indexer automatically adds a name for the object, based on the valueof the attribute, within the hierarchical namespace represented by thegraph of directories in the database. Referring again to FIG. 4, aprogram object may have both an “actor” attribute with value “JohnWayne” and a “director” attribute with value “John Ford” 401. The rootdirectory might indicate two sub-directories, “byactor” 402 and“bydirector” 403. The indexer would then add the paths “/byactor/JohnWayne” and “/bydirector/John Ford” to the database, both of which referto the same object 401.

A derived attribute is maintained for each object listing the directoryobjects which refer to this object 404. As the indexer adds paths to thenamespace for this object, it adds the final directory ID in the path tothis list. This insures closure of the object graph—once the object hasbeen found, all references to that object within the database are alsofound, whether they are paths or dependencies.

This unique and novel method of adding objects to the database hassignificant advantages over standard approaches. The indexer sorts theobject into the database when it is added. Thus, the search for theobject associated with a particular path is a sequence of selectionsfrom ordered lists, which can be efficiently implemented by one familiarwith the art.

Deleting Objects from the Database

While the rules for adding objects to the database are important, therules for removing objects from the database are also important inmaintaining consistency and accuracy. For example, if there were norobust rules for removing objects, the database might grow unboundedlyover time as obsolete objects accumulate.

The cardinal rule for deleting objects from the database is based onreference counting; an object whose reference count drops to zero issummarily deleted. For instance, this means that an object must eitherbe referred to by a directory or some other object to persist in thedatabase. This rule is applied to all objects in the closed dependencygraph based on the object being deleted. Thus, if an object which refersto other objects (such as a directory) is deleted, then the referencecount on all objects referred to is decremented, and those objectssimilarly deleted on a zero count, and so forth.

There is also an automatic process which deletes objects from thedatabase called the “reaper”. Periodically, the reaper examines allobjects in the database, and depending on the object type, furtherexamines various attributes and attribute values to decide if the objectshould be retained in the database. For example, the expirationattribute may indicate that the object is no longer valid, and thereaper will delete the object.

In the preferred embodiment, using a method similar to (or perhapsidentical to) the filtering and indexing methods described above, thereaper may instead access a reaper object associated with the objecttype of the current object, which may contain executable code of variouskinds, perhaps a sequence of executable commands. This code examines theattributes and attribute values of the current object, and determines ifthe object should be deleted.

The overhead of individually deleting every object for which thereference count has been decremented to zero may be quite high, sinceevery such deletion results in a transaction with the database. It wouldbe advantageous to limit the performance impact of reaping objects, suchthat foreground operations proceed with maximum speed. In a preferredembodiment, this is accomplished using a technique based on commongarbage collection methods.

For instance, instead of deleting an object whose reference count hasbeen decremented to zero, the reaper performs no other action.Periodically, a background task called the garbage collector examineseach object in the database. If the object has a reference count ofzero, it is added to a list of objects to be deleted. In one embodiment,once the garbage collector has examined the entire database, it woulddelete all such objects in a single transaction. One familiar in the artwill appreciate that this method may also result in a significantperformance penalty, as other accesses to the database may be delayedwhile the objects are being deleted. In addition, if all objects are tobe properly deleted, changes to the database may have to be delayedwhile the garbage collector is active, resulting in even worseperformance.

In a preferred embodiment, the garbage collector examines the databasein a series of passes. Once a specific number of objects has beencollected, they are deleted in a single transaction. Said processcontinues until all objects have been examined. This technique does notguarantee that all garbage objects are collected during the examinationprocess, since parallel activities may release objects previouslyexamined. These objects will be found, however, the next time thegarbage collector runs. The number of objects deleted in each pass isadjustable to achieve acceptable performance for other databaseactivities.

Operations on the Distributed Television Viewing Object DatabaseConsiderations in Maintaining the Distributed Viewing Object Database

The replication of television viewing objects among the instances of thedistributed database necessarily requires the transmission of objectsover unreliable and unsecure distribution channels.

For example, if the objects are transmitted over a broadcast mechanism,such as within a radio or television transmission, there can be noassurance that the data is transmitted accurately or completely.Weather, such as rainstorms, may cause dropouts in the transmission.Other sources of interference may be other broadcast signals, heavyequipment, household appliances, etc.

One skilled in the art will readily appreciate that there are standardtechniques for managing the transmission of data over unreliablechannels, including repeated transmissions, error correcting codes, andothers, which may be used for transmission, any or all of which may beused in any particular instance.

For efficiency, objects to be replicated are gathered together intodistribution packages, herein called “slices”. A slice is a subset ofthe television viewing object database which is relevant to clientswithin a specific domain, such as a geographic region, or under thefootprint of a satellite transmitter.

Security of these slices is quite important. Slices are used to addobjects to the database which are used to provide valuable services tousers of the database, as well as to store information that may beconsidered private or secret. Because of the broadcast-oriented natureof slice transmission, slices may be easily copied by third parties asthey are transmitted. A practical solution to these problems is toencrypt the slice during transmission. An ideal reference text on thetechniques employed in the invention is “Applied Cryptography:Protocols, Algorithms, and Source Code in C” by Bruce Schneier, JohnWiley and Sons, 1995.

In a preferred embodiment of the invention, a secure, encrypted channelis established using techniques similar to those described in U.S. Pat.No. 4,405,829, often described as asymmetric key encryption, orsometimes public/private key pair encryption. A practitioner skilled inthe art will recognize that protocols based on asymmetric key encryptionserves as a reliable and efficient foundation for authentication ofclient devices and secure distribution of information. In general,authentication is provided using an exchange of signed messages betweenthe client and central systems. Secure distribution is provided byencrypting all communications using a short-lived symmetric key sentduring an authentication phase.

Successful security requires that sender and receiver agree beforehandon the asymmetric key pair to be used for encryption. Such keydistribution is the weakest link in any cryptographic system forprotecting electronic data. U.S. Pat. No. 6,385,739, entitled “Self-TestElectronic Assembly and Test System,” filed Jul. 19, 1999, also owned bythe Applicant and incorporated herein by reference, describes amechanism whereby the client device generates the asymmetric key pairautomatically as the final step in the manufacturing process. Theprivate key thus generated is stored within a secure microprocessorembedded within the client device, such that the key is never presentedto external devices. The public key thus generated is transmitted to alocal manufacturing system, which records the key along with the clientserial number in a secure database. This database is later securelytransmitted to the central distribution system, where it is used toperform secure communications with the client.

This unique and novel application of key generation solves the problemof key distribution, as the private key is never presented to externalcomponents in the client, where it might be discerned using specialtools, such as a logic analyzer. Instead, it may only be used within thesecurity microprocessor itself to decrypt messages originally encryptedwith the public key, the results of which are then provided to externalcomponents.

The remainder of this discussion assumes that all communications betweenclient and central systems are authenticated and encrypted as describedabove.

Transmitting Viewing Objects to the Client Systems

Referring again to FIG. 1, in a preferred embodiment of the inventionthe following steps constitute “transmission” of television viewingobjects from the central database using slices:

-   1. There may be many mechanisms for transmitting slices to the    universe of client viewing devices. For instance, the slices may be    directly downloaded over a telephone modem or cable modem 109, they    may be modulated into lines of the Vertical Blanking Interval (VBI)    of a standard television broadcast 108, or added to a digital    television multiplex signal as a private data channel. One skilled    in the art will readily appreciate that any mechanism which can    transmit digital information may be used to transmit slices of the    television viewing object database.    -   The first step in preparing television viewing objects for        transmission is recognizing the transmission mechanism to be        used for this particular instance, and creating a slice of a        subset of the database that is customized for that mechanism.        For example, the database may contain television viewing objects        relating to all programs in the country. However, if television        viewing objects are to be sent using VBI modulation on a local        television signal, only those television viewing objects        relating to programs viewable within the footprint of the        television broadcast being used to carry them should be        contained within the relevant slice. Alternatively, if some of        the television viewing objects contain promotional material        related to a particular geographic region, those objects should        not be transmitted to other geographic regions.    -   In a preferred embodiment of the invention, the speed and        periodicity of traversing the database and generating slices for        transmission is adjustable in an arbitrary fashion to allow        useful cost/performance tradeoffs to be made. For instance, it        may only be necessary to create slices for certain transmission        methods every other day, or every hour.    -   The final step in preparing each slice is to encrypt the slice        using a short-lived symmetric key. Only client devices which        have been authenticated using secure protocols will have a copy        of this symmetric key, making them able to decrypt the slice and        access the television viewing objects within it.-   2. Once a slice is complete, it is copied to the point at which the    transmission mechanism can take and send the data 110. For telephone    connections, the slice is placed on a telephony server 111 which    provides the data to each client as it calls in. If television    broadcast is used, the slice is copied onto equipment co-resident    with the station television transmitter, from whence it is modulated    onto the signal. In these and similar broadcast-oriented cases, the    slice is “carouseled”, i.e., the data describing the slice is    repeated continually until a new slice is provided for transmission.    -   This repetitive broadcast of slices is required because there        can be no assurance that the signal carrying the data arrives        reliably at each client. The client device may be powered off,        or there may be interference with reception of the signal. In        order to achieve a high degree of probability that the        transmitted slices are properly received at all client devices,        they are continually re-broadcast until updated slices are        available for transmission.    -   A preferred embodiment of the invention uses broadcast        mechanisms such as a television signal to transmit the slice.        However, it is desirable to provide for download over a        connection-based mechanism, such as a modem or Internet        connection. Using a connection-based mechanism usually results        in time-based usage fees, making it desirable to minimize the        time spent transmitting the slice.    -   This is accomplished using a two-step process. When the        connection is established, the client system sends an inventory        of previously received slices to telephony servers 111. The        server compares this inventory with the list of slices that        should have been processed by that client. Slices which were not        processed are transmitted to the client system.-   3. The slice is transmitted by breaking the encrypted slice into a    succession of short numbered data packets. These packets are    captured by client systems and held in a staging area until all    packets in the sequence are present. The packets are reassembled    into the slice, which is then decrypted. The television viewing    objects within the slice are then filtered for applicability,    possibly being added to the local television viewing object    database. This process replicates a portion of the central database    of television viewing objects reliably into the client.    -   The invention keeps track of the time at which data packets are        received. Data packets which are older than a selected time        period are purged from the staging area on a periodic basis;        this avoids consuming space for an indefinite period while        waiting for all parts of a slice to be transmitted.    -   Especially when transmitting the objects over a broadcast        medium, errors of various kinds may occur in the transmitted        data. Each data packet is stamped with an error detecting code        (a parity field or CRC code, for example). When an error is        detected the data packet is simply discarded. The broadcast        carousel will eventually retransmit the data packet, which is        likely to be received properly. Slices of any size may thus be        sent reliably; this is achieved at the cost of staging received        portions of the object on the client until all portions are        properly received.-   4. There may be one or more “special” slices transmitted which    communicate service related data to the client system, particularly    service authorization information. It is important that the service    provider be able to control the client system's access to premium    services if the viewer has failed to pay his bill or for other    operational reasons.    -   One particular type of special slice contains an “authorization”        object. Authorization objects are generally encrypted using        asymmetric key encryption based on the public/private key pair        associated with a specific client. If the slice can be        successfully decrypted by the security microprocessor using the        embedded private key, the slice will contain an object        indicating the allowable time delay before another authorization        object is received, as well as one or more symmetric keys valid        for a short time period. The delay value is used to reset a        timestamp in the database indicating when the client system will        stop providing services. The symmetric keys are stored in the        local television viewing object database, to be used in        decrypting new slices which may be received.    -   If the client has not received a proper authentication object by        the time set in the database, it will commence denial of most        services to the viewer (as specified by the service provider).        Also contained within an authentication object are one or more        limited-lifetime download keys which are needed to decrypt the        slices that are transmitted. Clearly, if a client system is        unable to authenticate itself, it will not be able to decrypt        any objects.    -   Each authorization slice is individually generated and        transmitted. If broadcast transmission is used for the slices,        all relevant authorizations are treated identically to all other        slices and carouseled along with all other data. If direct        transmission is used, such as via a phone connection, only the        authentication slice for that client is transmitted.-   5. Once the client device has received a complete database slice, it    uses the methods described earlier to add the new object contained    within it to the database.    Collecting Information from the Client Systems

Referring again to FIG. 1, in a preferred embodiment of the inventionthe following steps constitute “collection” of television viewingobjects from each client database:

-   1. As the viewer navigates the television channels available to him,    the client system records interesting information, such as channel    tuned to, time of tuning, duration of stay, VCR-like actions (e.g.,    pause, rewind), and other interesting information. This data is    stored in a local television viewing object.    -   Additionally, the viewer may indicate interest in offers or        promotions that are made available, or he may indicate a desire        to purchase an item. This information is also recorded into a        local television viewing object.    -   Additionally, operation of the client device may result in        important data that should be recorded into a television viewing        object. For example, errors may occur when reading from the hard        disk drive in the client, or the internal temperature of the        device may exceed operational parameters. Other similar types of        information might be failure to properly download an object,        running out of space for various disk-based operations, or rapid        power cycling.-   2. At a certain time, which may be immediate or on a periodic basis,    the client system contacts the central site via a direct connection    104 (normally via phone and/or an Internet connection). The client    device sends a byte sequence identifying itself which is encrypted    with its secret key. The server fetches the matching television    viewing object for the client device from the database, and uses the    key stored there to decrypt the byte sequence. At the same time, the    server sends a byte sequence to the client, encrypted in its secret    key, giving the client a new one-time encryption key for the    session.    -   Both sides must successfully decrypt their authentication        message in order to communicate. This two-way handshake is        important, since it assures both client and server that the        other is valid. Such authentication is necessary to avoid        various attacks that may occur on the client system. For        example, if communications were not authenticated in such a        fashion, a malicious party might create an “alias” central site        with a corrupt television viewing object database and provide        bad information to a client system, causing improper operation.        All further communication is encrypted using the one-time        session key. Encrypted communication is necessary because the        information may pass across a network, such as the Internet,        where data traffic is open to inspection by all equipment it        passes through. Viewing objects being collected may contain        information that is considered private, so this information must        be fully protected at all times.    -   Assuming that the authentication phase is successful, the two        parties treat the full-duplex phone line as two one-way        broadcast channels. New slices are delivered to the client, and        viewing data to be collected is sent back. The connection is        ended when all data is delivered.    -   One skilled in the art will readily appreciate that this        connection may take place over a network, such as the Internet        running standard TCP/IP protocols, transparently to all other        software in the system.-   3. Uploaded information is handled similarly by the server; it is    assumed to represent television viewing objects to be replicated    into the central database. However, there may be many uploaded    viewing objects, as there may be many clients of the service.    Uploaded objects are therefore assigned a navigable attribute    containing information about their source; the object is then    indexed uniquely into the database namespace when it is added.    -   Uploaded viewing objects are not immediately added to the        central database; instead they are queued for later insertion        into the database. This step allows the processing of the queue        to be independent of the connection pattern of client devices.        For instance, many devices may connect at once, generating a        large number of objects. If these objects were immediately added        to the central database, the performance of all connections        would suffer, and the connection time would increase. Phone        calls are charged by duration, thus any system in which        connection time increases as a function of load is not        acceptable.    -   Another advantage of this separation is that machine or network        failures are easily tolerated. In addition, the speed at which        viewing objects are processed and added to the central database        may be controlled by the service provider by varying the        computer systems and their configurations to meet cost or        performance goals.    -   Yet another advantage of this separation is that it provides a        mechanism for separating data collected to improve service        operations and data which might identify an individual viewer.        It is important that such identifying data be kept private, both        for legal reasons and to increase the trust individuals have in        the service. For instance, the navigable attribute assigned to a        viewing object containing the record of a viewer's viewing        choices may contain only the viewer's zip code, meaning that        further processing of those objects can construct no path back        to the individual identity.    -   Periodic tasks are invoked on the server to cull these objects        from the database and dispose of them as appropriate. For        example, objects indicating viewer behavior are aggregated into        an overall viewer behavior model, and information that might        identify an individual viewer is discarded. Objects containing        operational information are forwarded to an analysis task, which        may cause customer service personnel to be alerted to potential        problems. Objects containing transactional information are        forwarded to transaction or commerce systems for fulfillment.    -   Any of these activities may result in new television viewing        objects being added to the central database, or in existing        objects being updated. These objects will eventually be        transmitted to client devices. Thus, the television viewing        management system is closed loop, creating a self-maintaining        replicated database system 105 which can support any number of        client systems.

Processing of Television Viewing Objects by Client Systems

Television viewing objects may contain the following types ofinformation: television program descriptions and showing times; cable,satellite or broadcast signal originator information, such as channelnumbering and identification; viewer preference information, such asactors, genre, showing times, etc.; software, such as enhanced databasesoftware, application software, operating system software, etc.;statistical modeling information such as preference vectors, demographicanalysis, etc.; and any other arbitrary information that may berepresented as digital data.

Methods Applied to Program Guide Objects

Program guide objects contain all information necessary for softwarerunning in the client system to tune, receive, record and view programsof interest to the user of the client system, selecting from among allavailable programs and channels as described by objects within thedatabase.

This program guide information is updated on a regular basis by aservice provider. This is handled by the provider acquiring programguide information in some manner, for instance, from a commercialsupplier of such information or other sources of broadcast scheduleinformation. This data is then processed using well-understood softwaretechniques to reduce the information to a collection of inter-relatedviewing objects.

Referring again to FIG. 4, a typical relationship between program guideobjects is shown. A television “network” object 407 is any entity whichschedules and broadcasts television programming, whether that broadcastoccurs over the air, cable, satellite, or other suitable medium. Atelevision “program” object 401 is a description of any distinct segmentof a television broadcast signal, such as a particular program,commercial advertisement, station promotion, opener, trailer, or anyother bounded portion of a television signal. A “showing” object 406 isa portion of the broadcast schedule for a network on which a program isbroadcast. A “channel map” object maps a network broadcast onto aparticular broadcast channel for the medium being used; for instance, achannel map object for a satellite broadcast service would includeinformation about the transponder and data stream containing thebroadcast. Using the previously described methods, this program guidedata is replicated from the central site to the client systems, whereapplication software in the client systems use the data to managetelevision viewing.

The service provider may also provide aggregation viewing objects, whichdescribe a set of program guide objects that are interrelated in somefashion. For instance, a “Star-Trek” collection might contain referencesto all program guide objects associated with this brand name. Clearly,any arbitrary set of programs may be aggregated in this fashion.Aggregation objects are similar to directories. For instance, the StarTrek collection might be found at “/showcases/Star Trek” in thehierarchical namespace. Aggregation objects are also program guideobjects, and may be manipulated in a similar fashion, includingaggregating aggregation objects, and so forth.

The client system may further refine the collection of program objects.In a system where programming may be captured to internal storage, eachcaptured program is represented by a new program guide object, becomingavailable for viewing, aggregation, etc. Explicit viewer actions mayalso result in creation of program guide objects. For instance, theviewer may select several programs and cause creation of a newaggregation object.

This description of types of program guide objects is not meant to beinclusive; there may be many different uses and ways of generatingprogram guide objects not herein described which still benefit from thefundamental methods of the invention.

Program guide objects are used by the application software in five ways:

-   1. In the simplest case, the viewer may wish to browse these objects    to discern current or soon-to-be-available programming. The    application software will map the object relationships described by    the database to some form of visual and audible interface that is    convenient and useful for the viewer. The viewer may indicate that a    particular program is of interest, resulting in some    application-specific action, such as recording the program to local    storage when it is broadcast.-   2. Application software may also directly process program guide    objects to choose programs that may be of interest to the viewer.    This process is typically based on an analysis of previously watched    programming combined with statistical models, resulting in a    priority ordering of all programs available. The highest priority    programs may be processed in an application specific manner, such as    recording the program to local storage when it is broadcast.    Portions of the priority ordering so developed may be presented to    the viewer for additional selection as in case 1.    -   One skilled in the art will readily appreciate that there is a        great deal of prior art centered on methods for selecting        programming for a viewer based on previous viewing history and        explicit preferences, e.g., U.S. Pat. No. 5,758,257. The methods        described in this application are unique and novel over these        techniques as they suggest priorities for the capture of        programming, not the broadcast or transmission of programming,        and there is no time constraint on when the programming may be        broadcast. Further details on these methods are given later in        this description.    -   In general, explicit viewer choices of programming have the        highest priority for capture, followed by programming chosen        using the preference techniques described herein.-   3. A client system will have a small number of inputs capable of    receiving television broadcasts or accessing Web pages across a    network such as an intranet or the Internet. A scheduling method is    used to choose how each input is tuned, and what is done with the    resulting captured television signal or Web page.    -   Referring to FIG. 6, generally, the programs of interest to the        viewer may be broadcast at any time, on any channel, as        described by the program guide objects. Additionally, the        programs of interest may be Web page Universal Resource Locators        (URL) across a network, such as an intranet or the Internet. The        channel metaphor is used to also describe the location, or URL,        of a particular Web site or page.    -   A viewer, for example, can “tune” into a Web site by designating        the Web site URL as a channel. Whenever that channel is        selected, the Web site is displayed. A Web page may also be        designated as a program of interest and a snapshot of the Web        page will be taken and recorded at a predetermined time.    -   The scheduler accepts as input a prioritized list of program        viewing preferences 603, possibly generated as per the cases        above. The scheduling method 601 then compares this list with        the database of program guide objects 604, which indicate when        programs of interest are actually broadcast. It then generates a        schedule of time 607 versus available storage space 606 that is        optimal for the viewer's explicit or derived preferred programs.        Further details on these methods are given later in this        description.-   4. When a captured program is viewed, the matching program guide    object is used to provide additional information about the program,    overlaid on the display using any suitable technique, preferably an    On Screen Display (OSD) of some form. Such information may include,    but is not limited to: program name; time, channel or network of    original broadcast; expiration time; running time or other    information.-   5. When live programming is viewed, the application uses the current    time, channel, and channel map to find the matching program guide    object. Information from this object is displayed using any suitable    technique as described above. The information may be displayed    automatically when the viewer changes channels, when a new program    begins, on resumption of the program after a commercial break, on    demand by the viewer, or based on other conditions.-   6. Using techniques similar to those described in case 2,    application software may also capture promotional material that may    be of interest to the viewer. This information may be presented on    viewer demand, or it may be automatically inserted into the output    television signal at some convenient point. For example, an    advertisement in the broadcast program might be replaced by a    different advertisement which has a higher preference priority.    Using the time-warping apparatus, such as that described in U.S.    Pat. No. 6,233,389 B1, entitled “Multimedia Time Warping System,”    filed Jul. 30, 1998, also owned by the Applicant and incorporated    herein by reference, it is possible to insert any stored program    into the output television signal at any point. The time-warping    apparatus allows the overlaid program to be delayed while the stored    program is inserted to make this work.

Methods for Generating a List of Preferred Programs

Viewer preferences may be obtained in a number of ways. The viewer mayrequest that certain programs be captured, which results in the highestpossible priority for those programs. Alternatively, the viewer mayexplicitly express preferences using appurtenances provided through theviewer interface, perhaps in response to a promotional spot for aparticular program, or even during the viewing of a program. Finally,preferences may be inferred from viewing patterns: programs watched,commercial advertisements viewed or skipped, etc.

In each case, such preferences must correspond to television viewingobjects stored in the replicated database. Program objects included awealth of information about each particular program, for example: title,description, director, producer, actors, rating, etc. These elements arestored as attributes attached to a program object.

Each individual attribute may result in the generation of a preferenceobject.

Such objects store the following information:

-   1. The type of the preference item, such as actor or director    preference;-   2. The weight of the preference given by the viewer, which might be    indicated by multiple button presses or other means;-   3. The statically assigned significance of the preference in    relation to other preferences, for example, actor preference are    more significant than director preferences;-   4. The actual value of the preference item, for instance the name of    the director.    With respect to FIG. 5, preference objects are stored in the    database as a hierarchy similar to that described for program guide    objects, however this hierarchy is built incrementally as    preferences are expressed 500. The hierarchy thus constructed is    based on “direct” preferences, e.g., those derived from viewer    actions or inferred preferences.    A similar hierarchy is developed based on “indirect” preferences    pointing to the same preference objects 501. In general, indirect    preferences are generated when preferences for aggregate objects are    generated, and are used to further weight the direct preferences    implied by the collection of aggregated objects. The preference    objects referenced through the indirect preference hierarchy are    generated or updated by enumerating the available program objects    which are part of the aggregate object 502, and generating or    updating preference objects for each attribute thus found.    The weight of a particular preference 503 begins at zero, and then a    standard value is added based on the degree of preference expressed    (perhaps by multiple button presses) or a standard value is    subtracted if disinterest has been expressed. If a preference is    expressed based on an aggregate viewing object, all preferences    generated by all viewing objects subordinate to the aggregated    object are similarly weighted. Therefore, a new weighting of    relevant preference elements is generated from the previous    weighting. This process is bounded by the degree of preference which    is allowed to be expressed, thus all weightings fall into a bounded    range.    In a preferred embodiment of the invention, non-linear combinations    may be used for weighting a preference item. For instance, using    statistical models provided by the central site, the client may    infer that a heavily weighted preference for three attributes in    conjunction indicates that a fourth attribute should be heavily    weighted as well.

The list of preferred programs is generated as follows:

-   1. A table 504 is constructed which lists each possible program    object attribute, and any preference objects for that attribute that    are present are listed in that entry.-   2. If the preference item is a string, such as an actor name, a    32-bit digital signature for that string is calculated using a    32-bit CRC algorithm and stored with the table item, rather than the    string itself. This allows for much faster scanning of the table as    string comparisons are avoided, at the slight risk of two different    strings generating the same digital signature.-   3. For each program object in the database, and for each attribute    of that program, the attribute is looked up in the table. If    present, the list of preference objects for that attribute is    examined for a match with the attribute of the current program    object. If a match occurs, the weight associated with that    preference object is added to weighting associated with the program    object to generate a single weight for the program.-   4. Finally, the program objects are rank-ordered based on the    overall weighting for each program, resulting in a list of    most-preferred to least-preferred programs.    Given this final prioritized list, a recording schedule is generated    using the methods described below, resulting in a collection of    recorded programs of most interest to the viewer.

Methods Applied to Scheduling Recording Versus Available Storage Space

As has been described previously, recorded programs will in general havean expiration date, after which the recorded program is removed fromclient storage. The viewer may at any time indicate that a programshould be saved longer, which delays expiration by a viewer-selectedinterval. The invention views the available storage for recordingprograms as a “cache”; unviewed programs are removed after a time, basedon the assumption they will not be watched if not watched soon afterrecording. Viewed programs become immediate candidates for deletion, onthe assumption they are no longer interesting.

With proper scheduling of recording and deletion of old programs, it ispossible to make a smaller storage area appear to be much larger, asthere is an ongoing flushing of old programs and addition of newprograms. Additionally, if resources are available, recordings may bescheduled of programs based on inferred preferences of the viewer; theseare called “fuzzy” recordings. This results in a system where theprogram storage area is always “full” of programming of interest to theviewer; no program is removed until another program is recorded in itsplace or the viewer explicitly deletes it.

Additionally, the viewer may select a program for recording at any time,and the recording window may conflict with other scheduled recordings,or there may not be sufficient space obtainable when the program must berecorded. The invention includes unique and novel methods of resolvingsuch conflicts.

Conflicts can arise for two reasons: lack of storage space, or lack ofinput sources. The television viewing system described herein includes afixed number of input sources for recording video and a storage medium,such as a magnetic disk, of finite capacity for storing the recordedvideo. Recording all television programs broadcast over any significantperiod of time is not possible. Therefore, resolving the conflicts thatarise because of resource limitations is the key to having the correctprograms available for viewing.

Referring again to FIG. 6, the invention maintains two schedules, theSpace Schedule 601 and the Input Schedule 602. The Space Schedule tracksall currently recorded programs and those which have been scheduled tobe recorded in the future. The amount of space available at any givenmoment in time may be found by generating the sum of all occupied space(or space that will be occupied at that time) and subtracting that fromthe total capacity available to store programs. Programs scheduled forrecording based on inferred preferences (“fuzzy” recordings) are notcounted in this calculation; such programs automatically lose allconflict decisions.

A program may be recorded 603 if at all times between when the recordingwould be initiated and when it expires, sufficient space is available tohold it. In addition, for the duration of the program, there must be aninput available from which to record it. The Input Schedule 602 tracksthe free and occupied time slots for each input source. In a preferredembodiment of the invention, the input sources may not be used foridentical services, e.g., one input may be from a digital televisionsignal and another from an analog television signal with differentprogramming. In this case, only those inputs from which the desiredprogram can be recorded are considered during scheduling.

With respect to FIG. 7, a flowchart is shown describing the steps takento schedule a recording in the preferred embodiment. First, an orderedlist of showings of the program of interest are generated 701. Althougha preferred embodiment of the invention orders these showings by time,such that the recording is made as soon as possible, any particularordering might be chosen. Each showing in this list 702 is then checkedto see if input 703 or space 704 conflicts occur as described above. Ifa showing is found with no conflicts, then the program is scheduled forrecording 705.

Otherwise, a preferred embodiment of the invention selects only thoseshowings of the program which have no input conflicts 706. Referringagain to FIG. 6, one can see that over the lifetime of a recording theamount of available space will vary as other programs are recorded orexpire. The list of showings is then sorted, preferably by the minimumamount of available space during the lifetime of the candidaterecording. Other orderings may be chosen.

Referring again to FIG. 7, for each candidate showing, the viewer ispresented with the option of shortening the expiration dates onconflicting programs 708, 709. This ordering results in the viewer beingpresented these choices in order from least impact on scheduled programsto greatest 707; there is no requirement of the invention that thisordering be used versus any other.

Should the viewer reject all opportunities to shorten expiration times,the final step involves selecting those showings with input conflicts710, and sorting these showings as in the first conflict resolutionphase 711. The viewer is then presented with the option to cancel eachpreviously scheduled recording in favor of the desired program 712, 713.Of course, the viewer may ultimately decide that nothing new will berecorded 714.

In a preferred embodiment of the invention, all conflicts are resolvedas early as possible, giving the viewer more control over what isrecorded. When the viewer makes an explicit selection of a program torecord, the algorithm described in FIG. 7 is used to immediatelyschedule the recording and manage any conflicts that arise.

Once an explicit selection has been made, and the viewer informed thatthe recording will be done, it will not be canceled without explicitapproval of the viewer.

Fuzzy recordings are periodically scheduled by a background task on theclient device. Given the prioritized list of preferred programs asdescribed earlier, the background scheduler attempts to schedule eachpreferred program in turn until the list is exhausted or no furtheropportunity to record is available. A preferred program is scheduled ifand only if there are no conflicts with other scheduled programs. Apreferred program which has been scheduled may be deleted under twoconditions: first, if it conflicts with an explicit selection, andsecond, if a change in viewer preferences identifies a higher priorityprogram that could be recorded at that time.

A further complication arises when handling aggregate viewing objectsfor which recording is requested. If conflict resolution was handledaccording to the method above for such objects, a potentially largenumber of conflicts might be generated, leading to a confusing andfrustrating experience for the viewer in resolving the conflicts. Thus,when aggregate objects are chosen for recording, conflicts areautomatically resolved in favor of the existing schedule.

In a preferred embodiment of the invention, conflicts resulting from therecording of aggregate objects will be resolved using the preferenceweighting of the programs involved; if multiple conflicts are caused bya particular program in the aggregate object, it will only be recordedif its preference exceeds that of all conflicting programs.

Methods Applied to Software Objects

The client system requires a complex software environment for properoperation. An operating system manages the interaction between hardwaredevices in the client and software applications which manipulate thosedevices. The television viewing object database is managed by a distinctsoftware application. The time-warping software application is yetanother application.

It is desirable to add new features or correct defects in these andother software subsystems which run on the client hardware device. Usingthe methods described herein, it is possible to replicate viewingobjects containing updated software modules into the client systemdatabase. Once present in the client system database, the followingunique and novel methods are used to install the updated software andcause the client system to begin executing the new software.

The software environment of the device is instantiated as a sequence ofsteps that occur when power is first applied to the device, each stepbuilding up state information which supports proper application of thefollowing step. The last step launches the applications which manage thedevice and interact with the viewer. These steps are:

-   1. A read-only or electrically programmable memory in the device    holds an initial bootstrap sequence of instructions. These    instructions initialize low-level parameters of the client device,    initialize the disk storage system, and load a bootstrap loader from    the disk into memory, to which execution is then passed. This    initial bootstrap may be changed if it resides in an electrically    programmable memory.-   2. The second stage boot loader then locates the operating system on    the disk drive, loads the operating system into memory, and passes    execution to the operating system. This loader must exist at a    specific location on the disk so as to be easily located by the    initial loader.

The operating system performs necessary hardware and softwareinitialization. It then loads the viewing object database software fromthe disk drive, and begins execution of the application. Otherapplication software, such as the time-warping software and viewerinteraction software, are also loaded and started. This software isusually located in a separate area on the disk from the object databaseor captured television programs.

Ideally, new software would be installed by simply copying it to theappropriate place on the disk drive and rebooting the device. Thisoperation is fraught with danger, especially in a home environment.Power may fail while copying the software, resulting in an inconsistentsoftware image and potential operating problems. The new software mayhave defects which prevent proper operation. A failure may occur on thedisk drive, corrupting the software image.

Although the methods of this invention have referred to a disk drive,one skilled in the art will readily appreciate that the methodsdescribed here apply generally to any persistent storage system. A diskdrive, and other persistent storage systems, are typically formattedinto a sequence of fixed-size blocks, called sectors. “Partitions” aresequential, non-overlapping subsets of this sequence which break up thestorage into logically independent areas.

With respect to FIG. 8, the invention maintains a sector of informationat a fixed location on the disk drive 803 called the “boot sector” 804.The boot sector 804 contains sufficient information for the initialbootstrap 801 to understand the partitioning of the drive 803, and tolocate the second stage boot loader 806.

The disk is partitioned into at least seven (7) partitions. There aretwo (2) small partitions dedicated to holding a copy of the second stageboot loader 806, two (2) partitions holding a copy of the operatingsystem kernel 807, two (2) partitions containing a copy of theapplication software 808, and a partition to be used as scratch memory809. For duplicated partitions, an indication is recorded in the bootsector 805 in which one of the partitions is marked “primary”, and thesecond is marked “backup”.

One skilled in the art will readily appreciate that, although twopartitions are described herein for redundancy, triple, quadruple orgreater degrees of redundancy can be achieved by creating moreduplicated partitions.

With respect to FIGS. 9a and 9b , on boot 901, the initial bootstrapcode reads the boot sector 902, scans the partition table and locatesthe “primary” partition for the second stage boot loader. It thenattempts to load this program into memory 903. If it fails 904, forinstance, due to a failure of the disk drive, the boot loader attemptsto load the program in the “backup” partition into memory 905. Whicheverattempt succeeds, the boot loader then passes control to the newlyloaded program, along with an indication of which partition the programwas loaded from 906.

Similarly, the second stage boot loader reads the partition table andlocates the “primary” operating system kernel 907. If the kernel can notbe loaded 908, the “backup” kernel is loaded instead 909. In any case,control is passed to the operating system along with an indication ofthe source partition, along with the passed source partition from above910.

Finally, the operating system locates the “primary” partition containingapplication software and attempts to load the initial application 911.If this fails 912, then the operating system locates the “backup”partition and loads the initial application from it 913. An indicationof the source partition is passed to the initial application, along withthe source partition information from the previous steps. At this point,application software takes over the client system and normal viewingmanagement behavior begins 914.

This sequence of operations provides a reasonable level of protectionfrom disk access errors. It also allows for a method which enables newsoftware at any of these levels to be installed and reliably broughtinto operation.

An “installer” viewing object in the object database is used to recordthe status of software installation attempts. It records the state ofthe partitions for each of the three levels above, including anindication that an attempt to install new software is underway 915. Thisoperation is reliable due to the transactional nature of the database.

Referring to FIG. 10, installing a new software image at any of thethree levels is handled as follows: the new software image is firstcopied into the appropriate backup partition 1001, and an indication ismade in the database that a software installation is underway 1002. Theprimary and backup partition indications in the partition table are thenswapped 1003, and the system rebooted 1004. Eventually, control will bepassed to the initial application.

Referring again to FIG. 9b , the first task of this application is toupdate the installer object. For each level 921, 922, the applicationchecks if an installation was in process 916, 917, and verifies that thelevel was loaded off of the primary partition 918. If so, theinstallation at that level was successful, and the installer object isupdated to indicate success for that level 919. Otherwise, theapplication copies the backup partition for that level over the primarypartition and indicates failure in the installer object for that level920. Copying the partition insures that a backup copy of known goodsoftware for a level is kept available at all times.

In a preferred embodiment of the invention, finalization of theinstallation for the top application level of software may be delayeduntil all parts of the application environment have been successfullyloaded and started. This provides an additional level of assurance thatall parts of the application environment are working properly beforepermanently switching to the new software.

Methods Applied to Operations Status Objects

Operations status objects are a class of viewing object in whichinformation about the usage, performance and behavior of the clientsystem is recorded. These objects are collected by the central sitewhenever communication with the central site is established.

The following operations status indicators are recorded for latercollection along with a time stamp:

-   1. Viewer actions, primarily pressing buttons on a remote control    device, are recorded. Each “button press” is recorded along with the    current time, and any other contextual information, such as the    current viewer context. Post-processing of this object at the    central site results in a complete trace of viewer actions,    including the context in which each action is taken.-   2. Automatic actions, such as beginning or ending the recording of a    program, or choosing a program to record based on viewer    preferences, are recorded. In addition, deletion of captured    programs is recorded. Post-processing of this object at the central    site results in a complete trace of program capture actions taken by    the client system, including the programs residing in the persistent    store at any point in time.-   3. Software installation actions, including reception, installation,    and post-reboot results are recorded.-   4. Hardware exceptions of various kinds, including but not limited    to: power fail/restart, internal temperature profile of the device,    persistent storage access errors, memory parity errors and primary    partition failures.    Since all actions are recorded along with a time stamp, it is    possible to reconstruct the behavior of the client system using a    linear time-based ordering. This allows manual or automatic methods    to operate on the ordered list of events to correlate actions and    behaviors. For instance, if an expected automatic action does not    occur soon after rebooting with new software, it may be inferred    that the new software was defective.

Processing of Television Viewing Objects by Central Site Systems Sourcesof Television Viewing Objects

A client system has a single source of television viewing objects: thecentral site. The central site object database has many sources oftelevision viewing objects:

-   1. Program guide information obtained from outside sources is    processed to produce a consistent set of program guide objects,    indicating “programs”, “showings”, “channels”, “networks” and other    related objects. This set of objects will have dependencies    (“channels” depend on “networks”, “showings” depend on “programs”)    and other interrelationships. When a complete, consistent set of    objects is ready, it is added to the database as an atomic    operation.-   2. New software, including new applications or revisions of existing    software, are first packaged into “software” viewing objects. As    above, the software may have interdependencies, such as an    application depending on a dynamically loaded library, which must be    reflected in the interrelationships of the software objects    involved. In another example, there may be two types of client    systems in use, each of which requires different software objects;    these software objects must have attributes present indicating the    type of system they are targeted at. Once a consistent set of    objects is available, it is added to the database as an atomic    operation.-   3. Each client system has a unique, secret key embedded within it.    The public key matching this secret key is loaded into a “client”    management object, along with other interesting information about    the client, such as client type, amount of storage in the system,    etc. These objects are used to generate authentication objects as    necessary.-   4. Aggregation program guide objects are added in a similar fashion.    In this case, however, the aggregation object must refer to    primitive program guide objects already present in the database.    Also attached to the aggregation object are other objects, such as a    textual description, a screen-based icon, and other informational    attributes. Once a consistent set of ancillary objects to the    aggregation is available, it is added to the database as an atomic    operation.-   5. Data collected from client systems.    It should be clear that there may be any number of sources of    viewing objects, and this enumeration simply shows the most basic    possible sources.

Operations on Television Viewing Objects

There are a large number of possible operations on the centraltelevision viewing object database. The following examples are meant toshow the type of processing that may be performed, however the potentialoperations are not limited to these examples:

-   1. Using various viewing objects, a number of interesting    statistical analysis tasks may be performed:    -   1.1. By examining large numbers of uploaded operations status        objects, it is possible to perform extensive analysis of        hardware reliability trends and failure modes. For instance, it        is possible to correlate internal temperature with expected MTBF        (Mean Time Between Failures) of client devices.    -   1.2. By examining large numbers of uploaded viewing information,        it is possible to derive demographic or psychographic        information about various populations of client devices. For        example, it is possible to correlate TV programs most watched        within specific zip codes in which the client devices reside.    -   1.3. Similarly, by examining large numbers of viewing        information objects, it is possible to generate “rating” and        “share” values for particular programs with fully automated        methods, unlike existing program rating methods.    -   1.4. There are many other examples of statistical analysis tasks        that might be performed on the viewing object database; these        examples are not meant to limit the applicability of the        invention, but to illustrate by example the spectrum of        operations that might be performed.-   2. Specialty aggregation objects may be automatically generated    based on one or more attributes of all available viewing objects.    -   Such generation is typically performed by first extracting        information of interest from each viewing object, such as        program description, actor, director, etc., and constructing a        simple table of programs and attributes. An aggregate viewing        object is then generated by choosing one or more attributes, and        adding to the aggregate those programs for which the chosen        attributes match in some way.    -   These objects are then included in the slices generated for        transmission, possibly based on geographic or other information.        Some example aggregates that might be created are:    -   2.1. Aggregates based on events, such as a major league football        game in a large city. In this case, all programs viewable by        client devices in or around that city are collected, and the        program description searched for the names of the teams playing,        coaches names, major player's names, the name of the ballpark,        etc. Matching program objects are added to the aggregate, which        is then sliced for transmission only to client devices in        regions in and around the city.    -   2.2. Aggregates based on persons of common interest to a large        number of viewers. For instance, an aggregate might be        constructed of all “John Wayne” movies to be broadcast in the        next week.    -   2.3. Aggregates based on viewing behavior can be produced. In        this case, uploaded viewing objects are scanned for elements of        common interest, such as types of programs viewed, actual        programs viewed, etc. For example, a “top ten list” aggregate of        programs viewed on all client devices in the last week might be        generated containing the following week's showing of those        programs.    -   2.4. Aggregates based on explicit selections by viewers. During        viewing of a program, the viewer might be presented with an        opportunity to “vote” on the current program, perhaps on the        basis of four perceived attributes (storyline, acting,        directing, cinematography), which generates viewing objects that        are uploaded later. These votes are then scanned to determine an        overall rating of the program, which is transmitted to those who        voted for their perusal.    -   2.5. There are many other examples of how the basic facilities        of this invention allow the service operator to provide        pre-sorted and pre-selected groups of related programs to the        user of the client device for perusal and selection. These        examples are not meant to limit the applicability of the        invention, but to illustrate by example the spectrum of        operations that might be performed.-   3. Manual methods may also be used to generate aggregate objects, a    process sometimes called “authoring”. In this case, the person    creating the aggregate chooses programs for explicit addition to the    aggregate. It is then transmitted in the same manner as above.

Clearly, aggregation program objects may also permit the expression ofpreferences or recording of other information. These results may beuploaded to the central site to form a basis for the next round ofaggregate generation or statistical analysis, and so on.

This feedback loop closes the circuit between service provider and theuniverse of viewers using the client device. This unique and novelapproach provides a new form of television viewing by providing uniqueand compelling ways for the service provider to present and promote theviewing of television programs of interest to individuals whilemaintaining reliable and consistent operation of the service.

Although the invention is described herein with reference to thepreferred embodiment, one skilled in the art will readily appreciatethat other applications may be substituted for those set forth hereinwithout departing from the spirit and scope of the present invention.Accordingly, the invention should only be limited by the Claims includedbelow.

1-20. (canceled)
 21. A method for storing a data object with dependencyinformation, the method comprising: generating a dependency attributefor a first data object, the dependency attribute comprising dependencydata indicative of a second data object, wherein the first data objectdepends on the second data object such that a client device requires thesecond data object to utilize the first data object; receiving, at theclient device, the first data object; determining, at the client device,whether the database stored on the client device contains the seconddata object; in response to determining that the database contains thesecond data object, storing the first data object in the database; inresponse to determining that the database does not contain the seconddata object: storing the first data object in a holding area; inresponse to determining that the first data object and the second dataobject are stored in the holding area, storing the first data object inthe database.
 22. The method of claim 21, further comprising: inresponse to determining that the first data object and the second dataobject are stored in the holding area, storing the second data object inthe database.
 23. The method of claim 22, wherein the first data objectand the second data object are stored in the database in a single atomictransaction.
 24. The method of claim 21, wherein generating thedependency attribute for the first data object comprises generating alist of all data objects that the client device requires to utilize thefirst data object.
 25. The method of claim 24, further comprising:determining, at the client device, whether the database stored on theclient device contains all data objects of the list; and in response todetermining that the database does not contain at least one of the dataobjects of the list: storing the first data object in the holding area;and in response to determining that the first data object and all dataobjects of the list are stored in the holding area, storing the firstdata object in the database.
 26. The method of claim 24, furthercomprising: in response to determining that the first data object andall data objects of the list are stored in the holding area, storing inthe database all objects that stored in the holding area.
 27. The methodof claim 26, wherein all objects that are stored in the holding area arestored in the database in a single atomic transaction.
 28. The method ofclaim 26, further comprising: maintaining a dependency graph for allobjects in the holding area and all objects in the database; and whereindata objects are stored in the database only when the dependency graphis closed.
 29. The method of claim 21, wherein the first object is ashowing object that comprises information describing a specific time ona specific television channel.
 30. The method of claim 29, wherein thesecond object is a program object that comprises information describinga specific television program.
 31. A system for storing a data objectwith dependency information, the system comprising: a client deviceconfigured to: generate a dependency attribute for a first data object,the dependency attribute comprising dependency data indicative of asecond data object, wherein the first data object depends on the seconddata object such that the client device requires the second data objectto utilize the first data object; receive the first data object;determine whether the database stored on the client device contains thesecond data object; in response to determining that the databasecontains the second data object, store the first data object in thedatabase; in response to determining that the database does not containthe second data object: store the first data object in a holding area;in response to determining that the first data object and the seconddata object are stored in the holding area, store the first data objectin the database.
 32. The system of claim 31, wherein the client deviceis further configured to: in response to determining that the first dataobject and the second data object are stored in the holding area, storethe second data object in the database.
 33. The system of claim 32,wherein the first data object and the second data object are stored inthe database in a single atomic transaction.
 34. The system of claim 31,wherein the client device is further configured, when generating thedependency attribute for the first data object, to generate a list ofall data objects that the client device requires to utilize the firstdata object.
 35. The system of claim 34, wherein the client device isfurther configured to: determine, at the client device, whether thedatabase stored on the client device contains all data objects of thelist; and in response to determining that the database does not containat least one of the data objects of the list: store the first dataobject in the holding area; and in response to determining that thefirst data object and all data objects of the list are stored in theholding area, store the first data object in the database.
 36. Thesystem of claim 34, wherein the client device is further configured to:in response to determining that the first data object and all dataobjects of the list are stored in the holding area, store in thedatabase all objects that stored in the holding area.
 37. The system ofclaim 36, wherein all objects that are stored in the holding area arestored in the database in a single atomic transaction.
 38. The system ofclaim 36, wherein the client device is further configured to: maintain adependency graph for all objects in the holding area and all objects inthe database; and store data objects in the database only when thedependency graph is closed.
 39. The system of claim 31, wherein thefirst object is a showing object that comprises information describing aspecific time on a specific television channel.
 40. The system of claim39, wherein the second object is a program object that comprisesinformation describing a specific television program.